Refining element

ABSTRACT

A pair of co-operating refining elements (10, 11) intended for a disc refiner with two opposed refining discs, one of which is stationary (stator) and the other one is rotary (rotor), for the working of lignocellulosic fiber material in a refining gap (12) between the co-operating refining elements (10, 11). The refining elements are provided with a pattern of bars (13-16) and intermediate grooves. Each bar is formed with a plurality of high bar portions (13, 15) and intermediate low bar portions (14, 16), counted in radial direction. High bar portions (13, 15) are located directly in front of low bar portions (14, 16) on opposed co-operating refining elements (10, 11). The length of the high bar portions (15) on refining elements (11) of the rotor exceeds the length of the high bar portions (13) on refining elements (10) of the stator.

FIELD OF THE INVENTION

The present invention relates to working and dispersing lignocellulosicfiber material, preferably wood pulp containing recycled fiber, duringthe refining thereof. More particularly, the present invention relatesto refining elements for use in disk refiners, intended for saidrefining.

BACKGROUND OF THE INVENTION

Known disk refiners generally comprise two opposed refining disks, whichare rotary relative to each other and on at least one of which aplurality of refining elements are arranged. These refining elements areformed with a pattern of bars and intermediate grooves. The refiningdisks are arranged so that a refining gap is formed between the refiningelements, through which the fiber material is intended to pass in anoutward direction therebetween. In this manner, the dispersing andrefining functions are carried out by the bars of the refining elements.

In the inner portion of the refining gap the refining elements aregenerally formed with coarse bars to initiate the disintegration of thefibrous material and to feed it outwardly to the outer portion of therefining gap, where working of the fibrous material takes place.

For the dispersing type of refining, the type of refiner is normallyused which comprises one stationary refining disk and one opposed rotaryrefining disk. This type of treatment, which is carried out on preheatedfiber material, which is generally present in high concentrations, hasthe object of utilizing lenient working to provide a pulp of improvedquality. The purpose of dispersing normally is to utilize mechanicaltreatment to unbind from the fibers in the pulp impurities, generally inthe form of printing ink and so-called hot-melts (plastic and glueparticles), and to disintegrate these impurities to a sub-visible sizewithout negatively affecting the fibers. The freeness (CSF) of the pulptherefore must not be appreciably reduced.

With conventional refining elements, which employ substantially radialbars in the refiner, capacity problems can arise when an effectiveworking of the fiber material is to be obtained. On the other hand,quality problems can arise when the capacity is increased. Furthermore,the freeness of the pulp is reduced. Also, while the tensile strengthcan certainly be improved thereby, the disintegration of impurities, orthe so-called speck reduction, will then be relatively poor.

By designing the refining elements with toothed working surfaces insteadof radial bars, a lenient working with good speck reduction is obtained.The freeness of the pulp is not reduced appreciably, and the strengthproperties of the pulp are affected only insignificantly.

SUMMARY OF THE INVENTION

In accordance with the present invention, these and other objects havenow been realized by the invention of apparatus for refininglignocellulose-containing material which comprises a first stationaryrefining disk having a first refining surface and a second rotatablerefining disk having a second refining surface, the first and secondrefining disks being mounted with the first and second refining surfacesfacing each other in opposed relationship thereby defining a refininggap therebetween, the first refining surface including a plurality ofradially extending first bars separated by a plurality of grooves andthe second refining surface including a plurality of radially extendingsecond bars separated by a plurality of grooves, the plurality ofradially extending first bars including a plurality of first raisedportions alternating radially with a plurality of first depressedportions, the plurality of radially extending second bars including aplurality of second raised portions alternating radially with aplurality of second depressed portions, the plurality of first raisedportions being located opposite the plurality of second depressedportions, and the plurality of second raised portions being locatedopposite the plurality of first depressed portions, the plurality offirst raised portions having a first predetermined length and theplurality of second raised portions having a second predeterminedlength, the first predetermined length being less than the secondpredetermined length.

In accordance with one embodiment of the apparatus of the presentinvention, the plurality of second raised portions includes an uppersurface forming an angle with respect to a plane parallel to the secondrefining surface such that the height of the plurality of second raisedportions increases in a direction radially outwardly within the refininggap.

In accordance with another embodiment of the apparatus of the presentinvention, the plurality of radially extending first bars includes aplurality of first wall portions separating the plurality of firstraised portions from the plurality of first depressed portions, theplurality of first wall portions being inclined with respect to adirection perpendicular to the first refining surface. In a preferredembodiment, the plurality of radially extending second bars includes aplurality of second wall portions separating the plurality of secondraised portions from the plurality of second depressed portions, theplurality of second wall portions being inclined with respect to adirection perpendicular to the second refining surface.

In accordance with the present invention, the cooperating refiningelements are designed in a manner which provides them with alternatinglyhigh and low bar portions resulting in effective speck reduction withoutappreciably reducing the freeness of the pulp while at the same timeimproving the strength properties of the pulp. In addition, a highcapacity can be maintained therewith.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be more fully appreciated with reference tothe following detailed description, which, in turn, refers to thedrawings in which:

FIG. 1 is a side, cross-sectional view of a pair of cooperating refiningelements in accordance with the present invention;

FIG. 2 is a front, elevational view of a stationary refining element inaccordance with the present invention;

FIG. 3 is a front, elevational view of a rotary refining element inaccordance with the present invention;

FIG. 4 is a graphical representation comparing the speck reduction as afunction of energy consumption for refining elements in accordance withthe present invention;

FIG. 5 is a graphical representation comparing the speck reduction as afunction of freeness for refining disks in accordance with the presentinvention; and

FIG. 6 is a graphical representation comparing tensile strength as afunction of energy consumption for refining elements in accordance withthe present invention.

DETAILED DESCRIPTION

Referring to the drawings, in which like reference numerals refer tolike elements thereof, FIG. 1 shows cooperating refining elements 10 and11, which are intended to be positioned on each of two opposed refiningdisks in a refiner where one of the refining disks is stationary and theother refining disk is rotary. One type of refining element 10 isintended for use in the stationary refining disk (stator), and the othertype of refining element is intended for use on the rotary refiningdisk. These cooperating opposed refining elements 10 and 11 definebetween them a refining gap 12, through which the fiber material is tobe passed outwardly from within, i.e. upwards in FIG. 1.

Each refining element 10 and 11 is provided with bars 13 and 14 and 15and 16, respectively, which extend substantially radially across thesurface of the refining elements. Alternatively, the bars can be angledin relation to the radius of the refining elements. Each bar is formedwith several high or elevated bar portions 13 and 15, respectively, andintermediate low or depressed bar portions 14 and 16, respectively,proceeding in the radial direction. The bars have a configuration suchthat high bar portions 13 and 15 are located directly in front of lowbar portions 14 and 16 on opposed refining elements. The high barportions 15 on the refining element 11 of the rotor have a length whichexceeds that of the high bar portions 13 on the refining element 10 ofthe stator, preferably by about 1.5 to 5 times, more preferably by about2 to 4 times. The transition between high and low bar portionspreferably consists of inclined surfaces. The height of the low barportions 14 and 16 can be in the range of a few millimeters, preferablyfrom about 0.5 to 2 mm.

In accordance with the embodiment shown in the drawings, the uppersurface on the high bar portions 15 on the refining element 11 of therotor forms an angle α with the direction of refining gap 12, i.e. withthe axial plane. This angle shall be such that the height of the barportions 15 increases as one moves radially outward. This angle α canvary, but preferably lies in the interval of from about 0° to 10°.Greater angles, however, can be used. The upper surface on the low barportions 14 of the stator can have a corresponding angle, in a mannersuch that the height of the bar portions 14 decreases as one movesoutwardly. The upper surface of the high bar portions 13 of the statorand the low bar portions 16 of the rotor, respectively, can also form anangle with the direction of the refining gap 12 in a similar way.

Due to the fact that the cooperating refining elements 10 and 11 areformed with alternatingly high and low bar portions 13 through 16, thefiber material is worked very effectively during its passage through therefining gap 12. By adjusting the refining gap, the axial distancebetween the bars can be changed, and at the same time the distancebetween opposed inclined transition surfaces between high and low barportions is changed. Cooperating refining elements can thereby be set sothat the tops of the bar portions work the fibers effectively andthereby improve the strength properties of the pulp, and at the sametime the inclined transition surfaces of the bar portions knead the pulpsoftly and force the pulp to move between the rotor and stator. Theworking of the pulp is rendered still more effective due to the angledupper surfaces of the bar portions.

At the same time that this highly effective working is achieved, a highcapacity is also maintained because the high bar portions 15 on therotor have a greater length than the high bar portions 13 on the stator.This configuration yields a high pump effect, and thus a high capacity.This also applies when the refining elements have a fine pattern, i.e.when the bars and grooves are narrow.

The present invention therefore clearly creates the possibility ofeffectively dispersing impurities without appreciably reducing thefreeness of the pulp, while at the same time the strength properties ofthe pulp can be improved and a high capacity could be maintained.

EXAMPLE

Refining elements according to the embodiment of the present inventionshown in the drawings were test run and compared to refining elementswith a conventional tooth-patterned working surface. The resultsobtained proved that refining elements according to the presentinvention yield a high speck reduction for a specified energyconsumption, and a specified reduction in the pulp freeness. A clearimprovement of the tensile strength of the pulp was also observed.Moreover, with refining elements according to the present invention, ahigher rate of production could be maintained.

The results appear from FIGS. 4-6, in which curve I refers to refiningelements of the present invention, and curve II refers to theconventional refining elements.

FIG. 4 shows the speck reduction in % for particles >50 μm as a functionof the specific energy consumption in kWh per ton bone dry pulp(kWh/BDT). FIG. 5 shows the speck reduction as a function of thefreeness decrease in ml CSF. FIG. 6 shows the increase in tensilestrength in % as a function of the energy consumption.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

We claim:
 1. Apparatus for refining lignocellulose-containing materialcomprising a first stationary refining disk having a first refiningsurface and a second rotatable refining disk having a second refiningsurface, said first and second refining disks being mounted with saidfirst and second refining surfaces facing each other in opposedrelationship thereby defining a refining gap therebetween, said firstrefining surface including a plurality of radially extending first barsseparated by a plurality of grooves and said second refining surfaceincluding a plurality of radially extending second bars separated by aplurality of grooves, said plurality of radially extending first barsincluding a plurality of first raised portions alternating radially witha plurality of first depressed portions, said plurality of radiallyextending second bars including a plurality of second raised portionsalternating radially with a plurality of second depressed portions, saidplurality of first raised portions being located opposite said pluralityof second depressed portions and said plurality of second raisedportions being located opposite said plurality of first depressedportions, said plurality of first raised portions having a firstpredetermined length and said plurality of second raised portions havinga second predetermined length, said first predetermined length beingless than said second predetermined length.
 2. The apparatus of claim 1wherein said plurality of second raised portions includes an uppersurface forming an angle with respect to a plane parallel to said secondrefining surface such that the height of said plurality of second raisedportions increases in a direction radially outwardly within saidrefining gap.
 3. The apparatus of claim 1 wherein said plurality ofradially extending first bars includes a plurality of first wallportions separating said plurality of first raised portions from saidplurality of first depressed portions, said plurality of first wallportions being inclined with respect to a direction perpendicular tosaid first refining surface.
 4. The apparatus of claim 3 wherein saidplurality of radially extending second bars includes a plurality ofsecond wall portions separating said plurality of second raised portionsfrom said plurality of second depressed portions, said plurality ofsecond wall portions being inclined with respect to a directionperpendicular to said second refining surface.